The most common clamping device in current use is the vice having a fixed jaw and a moving jaw carried by a threaded support engaged by a correspondingly threaded shaft for advancing the moving jaw to clamp a workpiece between the two jaws. Most vices are made from machined cast steel and must be bolted to a work bench or other support. For this reason, most vices are not easily portable from one working site to another.
A number of portable clamping devices have been proposed to enable a workman or handyman to conveniently transport the device from one work site to another. One such proposal is shown in European Patent Publication 64883 (82302408.8). This clamping device has an adjustable jaw which is fixed during the clamping operation, and a moving or clamping jaw actuated by a foot operated lever which pivots the jaw from a released position to a clamping position via an overcentring linkage pivoted to the lever and to the moving jaw to lock the moving jaw in its fully clamped position.
While the arrangement described in the above document has the advantage of portability, it does not allow different appropriate clamping forces to be applied depending on the object being clamped and the clamping range is not quickly adjustable, some degree of trial and error being required. Thus, unless the operator's foot is kept on the pedal to apply variable clamping forces lower than that necessary to cause the locking linkage to overcentre, only one clamping force may be maintained on a clamped object using this device, and this force may in many instances be excessive and damage the object being clamped or inadequate and allow the object to slip while being worked on.
Another type of clamping device is described in U.K. Patent Application 2187411. In the device shown in FIGS. 25 to 29, a moving jaw is operated by a spring loaded foot lever to apply a clamping force dictated by the force applied by the operator's foot. However, the operator's foot must be kept on the lever otherwise the spring releases the clamping jaw. This arrangement seriously restricts the activities which may be performed by the operator on the clamped object.
Numerous foot operated vices or clamps are disclosed in the Patent literature. For example, U.S. Pat. Nos. 1,430,260 Bobo and 2,892,369 Millet disclose clamps or vices having a foot operated lever which causes a work piece to be clamped between a fixed jaw and a movable jaw. While in each of these devices, the force applied by the foot operated lever may be varied, each device includes a toothed latching means for locking the foot operated lever when the required force has been reached. Since toothed locking devices can only be operated when the latch is aligned with an inter-tooth space, the foot operated lever cannot be locked at the desired position since the lever must be moved in either direction from the desired position to achieve the required alignment of the locking device. Furthermore, release of such locking devices often requires the foot operated lever to be pushed past its locked position thereby increasing the clamping force and possibly damaging the clamped object.